In a hydraulic brake system of the afore-described type wherein parts of the conduit system are closed by valves, a conventional change of pressure fluid will not be adequate to supply all areas of the brake system with fresh pressure fluid and maintain them free of air and gas bubbles, because a change of this type will only reach the brake conduit between the master brake cylinder and the given wheel brake for a supply with fresh pressure fluid. Especially in cases with a high content of water or dirt in the brake fluid, it must be ensured that the pressure fluid volume existing outside of the hydraulic fallback level is replaced by fresh pressure fluid. This measure will considerably enhance the safety of operation of an electrohydraulic brake system.
The published filling instruction ATE 520 24.46 discloses a brake fluid change or change of the pressure fluid. This filling instruction serves as a basis for directions for a brake fluid change, as carried out in workshops. This change is a so-called conventional change of the pressure fluid by way of manually applying the brake pedal several times, with the result that fresh pressure fluid is only substituted for the pressure fluid in the brake conduits between the master brake cylinder and the respective wheel brake.